Conventionally, in case an insulating material, e.g., of aluminum oxide (alumina), silicon nitride, and the like is formed into targets and sputter them so as to form an insulating film of oxides, nitrides and the like on that surface of a substrate to be processed which lies opposite to the target, it is known to use a sputtering apparatus (for example, see Patent Document 1).
This kind of sputtering apparatus is provided with: a vacuum chamber in which a target is detachably mounted in position; a stage which holds a substrate so that the substrate lies opposite to the target in the vacuum chamber; an isolating means for defining an isolated space in which the target and the substrate lie opposite to each other and which is isolated from an inside of the vacuum chamber; and an evacuating means which evacuates the inside of the vacuum chamber. In view of ease of maintenance and transferring of the substrates to the stage, and the like, it is normal practice to constitute the isolating means by assembling an isolating block and a plurality of isolating plates. The inside of the vacuum chamber and the inside of the isolated space are communicated with each other through the insulating block and through the clearance between the isolating plates. It is thus so arranged that the isolated space inside the vacuum chamber is evacuated accompanied by the evacuation in the vacuum chamber. In assembling the isolating block and the isolating plates together, the clearance between the isolating plates is set to a range of 2˜3 mm so that, when RF (radio frequency) power is applied to the target, a plasma does not leak through the clearance between the respective isolating plates.
By the way, during film formation by sputtering of the target, sputtered particles get adhered also to the isolating plates, resulting in contamination. Therefore, the isolating plates are replaced regularly. In case the isolating plates are not assembled to keep the above-mentioned clearance, the pressure in the isolated space at the time of film formation, and also plasma density will consequently be changed. As a result, in-plane film thickness and film quality distribution will be changed.
As a solution, it is conceivable to dispose a gauge head of a pressure sensor in the isolated space. In this arrangement, however, film formation will be made also on the surface of the gauge head and, therefore, measurement of the pressure at a high accuracy will no longer be possible. Therefore, conventionally the pressure inside the vacuum chamber (i.e., the space on the outside of the isolating plates) was measured and, based on this measured pressure, the pressure inside the isolated space used to be estimated.
However, in case the clearance between the respective isolating plates varies and consequently the pressure in the isolated space varies, deviation occurs between the pressure in the isolated space that was estimated as in the conventional example and the actual pressure in the isolated space. Therefore, there is a problem in that discrimination cannot be made as to whether the atmosphere in the vacuum chamber is in a state fit for film formation.